Novel 5-halo-1,3,2-oxazaphosphorine and 3-halo-1,5,2-oxazaphosphorine derivatives, which may serve as biological alkylating agents, are being synthesized for in vivo screening tests as improved anticancer drugs. The effect of isomer homogeneity on therapeutic activity of these compounds is being investigated by screening of isomerically pure samples. Resolution of cyclophosphamide into its optical isomers is also being pursued for similar screening studies. BIBLIOGRAPHIC REFERENCE: "Synthesis and Antitumor Activity of Cyclophosphamide Analogs. I. Benzo Annulated Cyclophosphamide and Related Systems", S. M. Ludeman and G. Zon, J. Med. Chem., 18, 1251 (1975).